TIME: To Keep Willpower from Flagging, Remember the F-Word: ‘Fun’

If you’re dieting, for instance, you may easily resist the blueberry muffin at that impossibly aromatic bakeshop you pass by in the morning. You may then have lunch with your friends but just order a small salad (sans creamy dressing, of course). But at some point later in the day, your defenses get weaker. You find yourself declaring after dinner that, yes, you will take a look at the dessert menu. I will have a slice of that creamy cheesecake, you say. After all, what’s a little indulgence after a strenuous day of healthful living? (More on Time.com: The ‘Other’ Salt: 5 Foods Rich in Potassium)

“Energy depletion effects are most apparent when people feel low autonomy,” says Richard M. Ryan, a psychology professor at the University of Rochester. “To the extent that activities are viewed as either fun or valuable, and therefore freely and willingly done, people find them less draining. And they can even experience increased energy [after] completion of such tasks.”